CHAPTER II 



Extent of the Leaf-Mining Habit 



economic species 



It is a matter of no little biological interest that the most 

 highly specialized and most numerous leaf -miners do little 

 harm to the plants whose leaves they inhabit. In such 

 great genera as Nepticula and Lithocolletis there are no 

 important economic species. These enter the leaf and feed 

 within it in such a way as to cause a minimum of disturbance 

 or of damage. These have found a way of living that lets 

 the leaf live also. These represent the acme of ecological 

 specialization. Their business is on a permanent basis. 

 They live in the same localities in the same plants in about 

 the same numbers year after year. 



One of these flat, legless, crossbanded, specialized larvae 

 with cell-shearing, sap-feeding mouth parts, Lithocolletis 

 guttifinitella, lives on poison ivy. It makes broad, tortuous, 

 whitish, upper surface mines, that take on shapes as varied 

 as those of water spilled on a smooth surface. These seem 

 to be spread over almost every leaflet in many ivy patches 

 in early autumn; yet the plants appear to be thriving. 

 Several larvae are at work together in nearly every mine. 

 When one sees how very abundant they can be in this 

 noxious plant, it seems almost a pity that their methods of 

 feeding injure that plant so little. 



The injurious species of leaf -miners are less specialized 

 and less steady going. They eat more of the leaf substance, 

 and they damage more than they eat. They disfigure their 

 host plants leaving them draped in seared, shrivelled, 

 tattered foliage. They are part-time leaf -miners, like the 



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